Conventionally, for instance, as described in Patent document 1, it is known that there is a device that suppresses resonance by controlling a torque outputted to a shaft of a vehicle driving system when the vehicle driving system resonates.
The device previously possesses map data formed by specifying by experiments in which region of a vehicle speed, a torque command value, or the like a resonance takes place. The device then estimates whether the resonance takes place in the vehicle based on the map data. When a shaft (or axle) of a front-wheel driving system or rear-wheel driving system is estimated to be resonating, the device decreases a torque outputted to the one driving system that is estimated to be resonating. Further, the device simultaneously increases a torque outputted to the other driving system that is not estimated to be resonating. This varies a torque ratio between the torques to the front wheel and the rear wheel, to thereby suppress the resonance.                Patent Document 1: JP-2002-78110A        
The invention described in Patent document 1 depends on a viewpoint that a vibration of a certain wheel or shaft is generated or varied by a driving force applied on the certain wheel or shaft. However, the vibration of the wheel or shaft has a close relationship with other parts, so that the vibration is sometimes generated by influence of the operations of the other parts. Namely, the vehicle body is disposed above the wheels via springs. The position of the vehicle body moves up and down, so that the springs expand and contract. This varies, of the wheels, grounding loads, i.e., forces that are upwardly and downwardly applied to the wheels, and thereby varies the rotational force of the wheels or shafts. The vibration is thereby generated.
In detail, accelerating of a vehicle generates such a phenomenon that the anterior portion of the vehicle relatively lifts up while the posterior portion of the vehicle falls down. Vice versa, decelerating of the vehicle generates such a phenomenon that the anterior portion of the vehicle falls down while the posterior portion of the vehicle lifts up. This varies the force affecting the individual wheels or shafts, resulting in generation of the vibration. Further, the variation of the force applied to the individual wheels or shafts vibrates the vehicle body, so that the shafts and vehicle body vibrate while affecting one another.
To prevent the vibration, for instance, it is possible that, after specifying individual relationships between the wheels (or shafts) and other parts of the vehicle, the driving force is adjusted based on the specified relationships. However, since the vehicle has a complicated structure, specifying of the entire relationships and subsequent compensating of them are very difficult. Therefore, it is preferable to adopt a different view that uniformly treats the causes generating the vibration and then execute compensation based on the view.